In office chairs, to enable a more comfortable seating position than chairs of the static type, they incorporate, in addition to a device for adjusting the height, the use of a device for the controlled swinging of the seat back or the seat plane and the seat back, generally located in the part immediately beneath the seat plane and integral to it. Each device is primarily activated via a protruding lever that can easily be gripped and therefore rotated in one direction or another, until the internal mechanism releases the articulation.
In short, it is therefore possible to maintain that the following are known:                1. Chairs in which the seat and seat back are designed with separate body shells, which are connected in such a way that an inclination of the seat back corresponds to a parallel downward movement of the seat plane;        2. Chairs in which only the seat back is freely swinging;        3. Chairs in which the raising of the seat plane corresponds to the inclination of the seat back;        4. Chairs in which both the seat and the seat back are individually adjustable;        5. Finally, seats in which both the seat plane and the seat back, which are interconnected, perform a synchronized inclination movement.        
Prior Art
By way of an example, a first dynamic device for chairs is described in FR2075176 (Suspa), involving a base equipped with a number of support arms, from which an upright rises, composed of a gas cylinder. The end of said gas cylinder, from which the activation button of the piston protrudes, is inserted inside a hole in the shape of a truncated cone, extracted monolithically from the containing box structure of the device.
U.S. Pat. No. 4,986,601 (Inoue) mentions a swinging mechanism to support a seat and the seat back of a chair, consisting of a central column that extends from the base of the chair, a first support clamp connected to the central column by means of a pedestal, a second support clamp connected to the chair and hinged to the first support clamp by means of a shaft, a third support clamp connected to the rear support and hinged by means of a shaft to the second support clamp, and a shaft that hinges the first support clamp to the third support clamp. U.S. Pat. No. 4,986,601 (Inoue) also provides for a gas piston with a valve that can be actuated by a rod in the central column to selectively adjust the height of the column. Finally, U.S. Pat. No. 4,986,601 (Inoue) also provides for spring mechanisms to exert an opposing force on the second support clamp, positioned between the first and second clamps.
DE0198056 (Neumuller) is of interest. This is a swinging mechanism to support the seat plane and seat back of a chair, consisting of a central column that extends from the base of the chair, a first support clamp connected to the central column, a second support clamp connected to the seat plane and pivoted to the first clamp by a first pivot, a third support clamp connected to the seat back and hinged to the second support clamp by a second pivot, in addition to a mechanism that pivots the first support clamp to the third support clamp. Finally, DE0198056 (Neumuller) provides for spring mechanisms positioned between the first and second support clamps, to exert an opposing force to the movement of the second clamp.
Prior Art Concerning the Subject of the Invention
EP0329455 (Aero) proposes a device to adjust the inclination and lock the back of a chair. In more detailed terms, this is a push-button device positioned along the external side and at the end of one of the two arms of an aircraft seat. Said button controls the running of a cable arranged coaxially to a sheath, integrated into the arm and extending along the same towards the back until it reaches the termination underneath the seat plane, where an actuator device is positioned. Said actuator device is composed of a cylinder which, on one side, provides the activation button stimulated by means of a set of levers, from the small cable connected to the button and, from the other side, activates, via the shaft, a movement arm controlled by the seat back.
Finally, U.S. Pat. No. 6,019,429 (Global) proposes a control device for a chair for office use. In this specific case, it is a question of at least one control button integrated into the arm of a chair, and more specifically located directly underneath the support plane afforded by the same arm, along the side and appearing towards the inside of the seat. In this hypothesis, the button is inserted coaxially to a support, consisting of a cylindrical guide body that can be implemented in the structure of the arm. Even more specifically, said support provides for the protrusion, on one side, of the button, which remains external with respect to the arm, and on the other side (internally to the arm), by means of a fork arrangement, locks, with the lower part of the same, the end of the sheath, from which the respective control cable emerges. The end of said control cable is implemented next to one end of an overhanging lever with an “L” arrangement. This lever is in turn pivoted, at the side, to the upper part of the fork, a little above the lower one. It usually consists of a pre-tensioned cable, which, by means of the lever, ensures that the button always protrudes towards the outside, enabling the user to activate the adjustment device by means of exerting a light pressure on the same, in such a way as to cause the swinging of the lever in an upward direction, which therefore subsequently pulls the control cable. To permit the activation of the cylinder, which in this case always controls the single function of locking/releasing the back, the other end of the flexible cable also uses a lever, which is pivoted, with a spring-back mechanism, at the side of the activation button located next to said movement cylinder of the back. In this way, with the button in the depressed position, the lever pivoted to the movement cylinder is brought considerably closer to the base that holds the end of the sheath, with the result that, by means of a denticle, the latter exerts a force on the activation button, thus controlling the exit of the shaft.
Disadvantages
In short, it is possible to maintain that the proposals referred to, U.S. Pat. No. 4,986,601 (Inoue) or even DE0198056 (Neumuller), on the other hand, solutions that are conceptually very similar in the effect of the interaction of the three clamps, require locking/release mechanisms which are rather complex, involving a large number of components. Even if one ignores this last aspect, which it can easily be imagined involves objective difficulties and warehouse management costs, the complex interaction between the components sometimes does not permit them to function optimally. That is to say that conditions can arise in which the mechanism, having been brought into the locking state, is engaged only along a small part of its length, with the consequence that an accidental release is always possible. In addition, this can be operated only by means of a lever positioned underneath the seat plane, which is particularly inconvenient for the user.
As regards the proposal U.S. Pat. No. 6,019,429 (Global) and EP0329455 (Aero), it is a matter of devices that operate only with the possibility of adjusting the seat back. In addition, to be activated in the release state, they require the user to maintain a certain pressure on the activation button, a condition which may involve a precarious balance for the user. Furthermore, it may occur that the user, when not supported by the back, suffers the effect of the sudden and violent return of the seat back to a forward position, which is a particularly annoying condition that gives rise to feelings of insecurity in the mind of the user, and a lack of confidence in the product.